This invention relates in general to the forming of perforation patterns in structures and, more specifically, to the manufacture of preformed maskant sheets useful in the production of perforated parts.
The manufacture of various structures from sheet materials such as metal or composites having patterns of closely spaced holes or perforations is well known. Such structures have many applications such as acoustic panels, aircraft and space structures where weight savings are important, and the like. These perforations have in the past been formed by a wide variety of methods.
Most commonly, such perforations are formed by conventional machining, using drilling or milling operations. While effective, these methods have been largely superseded due to the difficulty in supporting sheet structures having complex shapes during machining, slow production even with the use of ganged drills and the difficulty in producing large, precise, patterns of perforations which often requires elaborate and expensive numerically controlled machines.
Where the structural shape is not too complex, punched sheets of maskant material may be placed over the structure and the perforations formed by grit blasting, or electrical etching or the like. However, with complex shapes, the maskant sheet stretches, distorting the perforation pattern. Also, tooling for punching other than flat maskant sheets is complex and expensive.
Thus, there is a continuing need for improved methods and apparatus for making maskant sheets for use in the more advanced methods of forming perforations in a wide variety of materials and for forming structures having complex shapes.